In the electrolytic reduction of aluminium from the aluminium oxide dissolved In molten cryolite, fluorspar $\left({\mathrm{CaF}}_2\right)$ is added to

Alumina dissolved in fused cryolite is reduced electrolytically with the addition of a tiny amount of fluorspar (${\mathrm{CaF}}_2$) (${\mathrm{Na}}_3{\mathrm{AlF}}_6$). Cryolite and fluorspar are added to boost alumina's electrical conductivity and bring down the fusion temperature to about 1140 $\mathrm{K}$.